1394 mKKINCF.I.LA 



dorsal scars witliin tlie beak cavities, which are deep : nacre 

 white and very iridescent. 



Length 27, height 24, diam. 23 mm. 



Rio de la Plata ; Eastern Peru ? 

 Plagiodon isocardiodes Lea, Pr. Ac. N. Sci. Phila., VIH, 



1856, p. 79. 

 Plagiodon isocardioides Lea, Obs., \'I, 1857, p. 38, pi. xxxii, 



fig. 32; Jl. Ac. X. Sci. Phila., IH, 1858, p. 318, pi. xxxii, 



fig. 22- — Kusti-:k. Conch. Cab. Unio, 1862, p. 292. pi. xcvii, 



figs. 8-10. 

 Unio isocardioides Sowerby, Conch. Icon., XVL 1868, pi. xc,. 



fig. 484. 

 Margaron (Plagiodon) isocardioides Lea, Syn., 1870, p. 71. 

 Iheringella isocardioides Simpson, Syn., 1900, p. 913. 



The form of this shell is much like that of Isocardia inoltk- 

 iana as Lea remarks. The teeth are imperfect and somewhat 

 granulate or dentilate. 



Iheringl:i.i,a semisui.cata (PL Adams). 



Shell rhomboid, solid, ventricose, somewhat inequilateral ; 

 beaks incurved, but little elevated ; posterior ridge well devel- 

 oped, curved, lightly pinched up, ending in a blunt point at 

 the base of the shell ; dorsal outline almost evenly arched from 

 the beaks to the end of the posterior ridge ; anterior end evenly 

 rounded : base rounded in front, incurved behind the middle ; 

 surface rugoselv concentricallv striate, marked with radial 

 sculpture medially : epidermis subrugose, olivaceous, blackish ; 

 nacre pearly white, iridescent. 



Length 34, height 25, diam. t8 mm. 



Eastern Peru. 

 Monocondylcea (Plagiodon) semisitlcata H. Adaisfs, Pr. Zool. 



Soc. Lond., 1870, p. 376. pi. xxvii, fig. 3. 

 Iheringella semisidcaia Simpson, Syn., 1900, p. 913. 



Adams does not tell anything of the teeth of this species, 

 but states that he had referred a larger specimen, previously 

 seen, to Lea's P. isocardioides, but that on comparing speci- 



